1. Field of the Invention
The present invention relates generally to weighted diversity combiners and more particularly to such combiners utilizing both AGC and AM voltages from the AGC loops of a plurality of receivers for generating an optimum weighting signal.
2. Description of the Prior Art
It is frequently desirable to combine signals from a plurality of receivers arriving at a plurality of points in a manner which provides maximum SNR to a load. However, it is usually difficult to process these signals so as to provide maximum SNR to the load. This is due in part to the fact that phase relationships of the mean frequencies of a given spectrum or the carriers of the incoming signals are generally independent of each other. The addition, therefore, of the two or more of such signals provides an output whose amplitude is dependent upon the vector sum of the incoming signals and results in an output varying as a function of the phase and amplitude relationships of the incoming signals. For example, when signals obtained from each of a plurality of antenna elements are added, the power transformed therefrom depends upon the relative location of each antenna element with respect to the transmitting source. Also, in an antenna array, the spacing of elements becomes important as does the spacing of transducers in an acoustical array.
In other instances, the transmission medium may change to bring about undesirable phase differences in the incoming signals to be combined. While under certain conditions phase discrepancies may be corrected to permit maximum signal power transfer to a load which in some instances may be a diversity receiver, in other cases, the transmitting medium and the direction of the source may vary in a manner such that phase correction becomes difficult if not impossible to achieve.
It is therefore desirable to combine a plurality of separate signals of differing phase to achieve maximum power transfer to a load irrespective to the phase relationships between the incoming signals. It is also desirable to combine modulated signals from a common source to achieve maximum power output when such signals are received by a plurality of antenna elements. In other instances, it is required that signals from a plurality of antenna elements be combined in an efficient manner when frequency diversity transmission is employed. Finally, it may be desirable to combine in an efficient manner individual signals which contain the same information when received irrespective of the transmission or receiving medium.
A straightforward and simple procedure for optimumly combining three or more signals is not known to exist in the prior art. One combining procedure described in U.S. Pat. No. 3,609,663 entitled "Predetection Signal Processing System" by Bickford et al. is capable of combining three or more signals. However, this technique involves a regenerative process that is quite complex and suffers from limitations such as a limited dynamic range of input signals. In addition, the invention of Bickford et al. is inherently narrow band with feedback and feedforward paths and is therefore unable to accommodate a wide-bandwidth fading signal.